1. Field of the Invention
This invention relates to the separation of dispersed matter from a liquid or gaseous medium through the use of an electrostatic force. More particularly, the invention is directed to a new and improved method and apparatus for separating dispersed matter, consisting of finely-divided particles and/or any ionizable chemical species such as molecules, atoms and radicals (such species being hereinafter referred to as "molecular species"), from a fluid medium by means of an electrostatic repulsive force.
2. Description of the Prior Art
In the conventional electrostatic precipitation of particulate matter from a fluid medium, it is well understood that separation of the particulate matter in the fluid is achieved through the following three basic steps: (a) electrostatic charging of particulate matter with a discharging electrode, (b) collecting of the charged particulate matter with a grounded electrode, and (c) removal of the collected particulate matter from the grounded electrode. Since the ultimate separation of the particulate matter from the fluid is accomplished only when the collected particulate matter is removed from the collecting electrode and placed outside the electrostatic precipitator, the insufficient retention of the particulate matter in the applied field, and the re-entrainment into the fluid stream of particulate matter which already had been collected, would result in poor separation efficiencies.
The above two difficulties are minimized by the use of low fluid velocities, and by the continuous removal of the collected particulate matter from the collecting electrode. As a result of these limitations, however, the size, the complexity and the cost of an efficient electrostatic precipitator typcially are very great.
The so-called "electrostatic filter", such as one disclosed in U.S. Pat. No. 3,544,441, issued to E. A. Griswold on Dec. 1, 1970, may increase the degree of particle retention in the electrostatic field, and so reduce substantially the particle re-entrainment into the fluid. But, periodic removal of the collected material is required, as is frequent cleaning of the porous matrix which is used. Furthermore, due to the high concentration and long retention of the charged particles in the field near the collecting electrode, abnormal particle charging and resultant undesirable separation characteristics in the apparatus would be inevitable. These phenomena might include back corona discharge, the lowering of the spark-over voltage, the suppression of particle charging, and the like.
It is most important to note that, in every conventional electrostatic separation technique, the particulate matter is charged by the discharging electrode, and attracted to the collecting electrode by which the particles are separated from the fluid. In other words, the collecting electrode is acting as the separating electrode. It thus is the electrostatic attractive force between the charged particulate matter of one polarity and the collecting electrode of the other polarity that constitutes the driving force for the separation in accordance with conventional techniques. The electrostatic repulsive force is not utilized in any separation technique heretofore known. Therefore, molecular species other than those adsorbed on the collected particulate matter cannot be separated from the fluid medium, since the ionized molecular species would be neutralized on the collecting electrode and remain free within the fluid medium.